This invention relates in general to valves of the plug or rotor type. More specifically, it relates to an improved arrangement for sealing the rotor within its chamber that avoids binding due to contaminants or extreme temperature variations. This invention is an improvement over the plug valve with renewable sealing inserts described in U.S. Pat. No. 3,218,026 to Roy.
As stated in the Roy patent, rotor valves have a significant advantage over other types of valves in that they are generally top loaded. This greatly facilitates maintenance since the working parts of the valve are readily removed or assembled without disconnecting pipes from the valve or extensive disassembly of the valve itself.
In general, the valves have a rotor that rotates about its longitudinal axis in a rotor chamber or bore formed in a valve housing. The rotor has a transverse passage or passages that communicate between inlet and outlet ports when the valve is in an open position. When the rotor is rotated to a closed position, the rotor blocks a fluid flow through the valve. A central problem with this type of valve is how to establish an effective fluid seal between the mating surfaces of the rotor and the surrounding chamber while at the same time avoiding excessive wear, a high operating torque, and jamming or binding. It is also important that the rotor valve have a cost of manufacture that is competitive with alternative valve types.
One common rotor valve design is the plug cock valve which uses a tapered plug (or rotor) lapped to conform closely to the tapered walls of the valve chamber. This valve, however, is readily fouled by corrosion and is relatively expensive to manufacture due to the cost of machining the tapered plug and chamber surfaces to close tolerances.
The aforementioned U.S. Pat. No. 3,218,026 to Roy and U.S. Pat. No. 3,556,153 to Barbuto, both commonly assigned with the present application, describe rotor valves that address the problems discussed above by using sealing inserts or segments to establish a seal between the rotor and the surrounding valve chamber. In the valve described in applicant's U.S. Pat. No. 3,556,153, four curved sealing segments ride on the outer surface of a solid, cylindrical rotor. The segments are angularly spaced and secured rigidly in narrow, longitudinally extending grooves formed on the outer surface of the rotor. The space between the segments provides a wiping action to clean sediment from the mating fluid-sealing surfaces of the segments and the chamber. In the Roy valve, the sealing inserts are rigidly held in wide, longitudinally extending channels also formed on the outer surface of a cylindrical rotor. The outer surface of each insert is curved to mate with the wall of the valve chamber. The Roy inserts are either rigid and machined to close tolerances or resilient and slightly oversized.
Both the Roy sealing inserts and applicant's earlier sealing segments have a significant advantage over conventional rotor valves in that worn or defective sealing members are easily replaced at a comparatively low cost. Further, none of these sealing member valves require lubrication. They nevertheless have several drawbacks. First, they are susceptible to binding due to extreme temperature variations or the presence of contaminants that lodge between the sealing members and the rotor chamber wall. While applicant's U.S. Pat. No. 3,556,153 sealing segments do provide a wiping action, it is not sufficient in applications where there is an unusually high concentration of contaminants such as fine dust particles. Second, the resilient Roy sealing inserts wear readily and create a relatively high operating torque. Third, the rigid Roy sealing inserts do not conform to irregularities in the chamber wall to maintain a tight fluid seal with a minimum of wear.
In ball valves, it is known to use annular, washer-like, sealing members that are spring loaded to establish a fluid seal against the spherical outer surface of the ball. The sealing members however, do not establish a fluid seal over an extended curved surface, but rather what is substantially a line seal, typically circular in shape. The problems inherent in ball valve seals are therefore basically different from those faced in rotor valves. For example, the problem of machining mating surfaces to close tolerances and the binding, jamming, and operating torque problems in ball valves and rotor valves are quite different. It should also be noted that these ball valve sealing members are typically resilient and have a specially designed cross-sectional configuration adapted to establish a seal against a smooth, spherical surface. All of these differences are present in the ball valves described in U.S. Pat. Nos. 3,252,684; 3,472,270; 3,576,309; 3,604,682; 3,667,727; and 4,111,393.
U.S. Pat. Nos. 197,924; 2,545,220 and 3,967,811 describe rotor valves that include sealing arrangements where a resilient member such as a spring urges a contoured sealing element into mating contact with a rotor chamber wall. In these valves, however, this resilient member does not itself form a fluid-tight seal, nor does it hold the sealing elements tightly enough against the chamber wall to effect a seal in the absence of fluid pressure. U.S. Pat. No. 1,081,322 describes another rotor valve using spring loaded sealing elements. In this valve fluid pressure retracts one of two oppositely directed sealing elements to allow the passage of fluid between the retracted element and the rotor chamber wall. A major disadvantage of this sealing arrangement is that it introduces contaminants into the area between the sealing element and the chamber wall.
U.S. Pat. No. 2,371,657 describes another rotor valve with a spring loaded sealing assembly carried on the rotor and engaging a surrounding housing. This valve also differs from the usual rotor valve because every port has a sealing element which can, in response to sensed fluid pressure levels on both sides of the sealing element, block or pass a fluid flow through that port in either direction. The sealing assembly uses an internal O-ring. It, however, does not urge the sealing element into a seated, fluid sealing position with respect to the chamber wall. Also, the O-ring does not deform in response to the fluid pressure to enhance any fluid seal.
It is therefore a principal object of this invention to provide a sealing arrangement for a rotor valve that does not bind due to contaminants, particularly high concentrations of fine particulate contaminants, or temperature variations.
Another object of the invention is to provide such a rotor valve sealing arrangement that is easy to maintain, has a low-torque operating characteristic and accommodates irregularities in the valve chamber wall.
A further object is to provide a rotor valve with rigid sealing surfaces that has the foregoing advantages and has good wear characteristics.
Still a further object is to provide a rotor valve sealing arrangement which automatically enhances the seal in the presence of high fluid pressures.
Yet another object is to provide a rotor valve sealing arrangement with the foregoing advantages that also has a relatively low cost of manufacture.